1. Field of the Invention
The present invention relates to a storage medium with which data-recording or data-reproducing (or both) is performed optically or magneto-optically. The present invention also relates to an optical data processor for reading out information stored in such a recording medium.
2. Description of the Related Art
As known in the art, optical disks such as CDs and DVDs are provided with data-recording tracks. Each track extends circumferentially of the disk and is divided into a plurality of sectors. FIG. 20 of the accompanying drawings shows the sector arrangement of a conventional optical disk. As illustrated, each sector includes a data-recording region Z1 and an address region Z2. The data-recording region Z1 is used for data-writing. The recording method to be employed may be magnetic field modulation for example. The data-recording region Z1 is provided with a land L or groove G for the track T.
Referring to FIG. 21, a laser beam striking upon the land L or groove G is reflected and generates an zero-order ray Ro together with two first-order rays Re and Rf. The zero-order ray Ro is a non-diffracted ray that traces the incidence path of the laser beam, while the other rays Re and Rf are diffracted rays of first order that result from the alternate juxtaposition of the lands L and the grooves G in the tracking direction.
As shown in FIG. 21, the zero-order ray Ro interferes with the first-order rays Re and Rf, thereby producing two interference rays Ie and If in the tracking direction. When the tracking operation is not properly performed, the two interference rays Ie˜If will exhibit a difference in intensity of light. The conventional tracking control is performed based on the intensity difference between the two interference rays.
The address region Z2 (see FIG. 20) is provided with a fixed record of sector-specific address information. The address information is expressed by convex or con-cave marks or “pits” 90. The mark edge recording format is adopted, where the information pits 90 are modulated in length.
In recent years, the amount of data to be dealt with in computers, communications apparatus, audiovisual equipment, etc. has been increasing. Accordingly, much greater data-storing capacity is required for optical recording mediums. One way to achieve this is to make the address region Z2 as short as possible in the conventional disk described above, thereby increasing the ratio of the data-storing regions Z1 in the tracks.
However, the conventional information pits 90 are length-modulated, as stated above, and the two edges (leading edge and trailing edge) of each pit 90 only serve as a switching point between 0 and 1 in the binary system, whereby each information pit 90 cannot carry much information. Consequently, the address region Z2 tends to be long, whereas the data-recording regions tend to be shortened (deterioration of disk format utility).
In the conventional disk, the pitch between adjacent tracks T is made small for increasing the data-storing density. In this situation, as shown in FIG. 20, the information pits 90 in a first group Ga and a second group Gb are arranged serially in the track-extending direction in a manner such that the pits 90 of the first and the second groups Ga, Gb are staggered in the tracking direction by a distance Lp. Unfavorably, this arrangement is also a cause for the increased length of the address region Z2 (and hence the deterioration of disk format utility).